High-capacity V-/Sc-/Ti-doped MnO2 for Li/MnO2 batteries and structural changes at different discharge depths

Abstract

Pure and Sc2O3-, TiO2-, and V2O5-doped MnO2 were synthesized via ambient-temperature redox synthesis followed by ultrasonication. X-ray diffraction patterns show that pure and doped MnO2 samples all crystallize in the ϒ-MnO2 structure. Brunauer–Emmett–Teller (BET) analysis indicates higher surface areas for doped MnO2, and TiO2-doped MnO2 exhibits the highest surface area of 106.60 m2g−1. Compared with undoped MnO2, the electrochemical results demonstrate that all of the doped MnO2 samples have higher specific discharge capacities and voltage platforms, among which TiO2-doped MnO2 shows the highest capacity. The discharging efficiency of TiO2-doped MnO2 reaches 90.32% (278.2 mAh g−1) at 0.1mAcm−2 and 73.02% (224.9 mAh g−1) at 2.0mAcm−2. In addition, the electrode fabricated from this material displays a greater improvement in its electrochemical lithium-storage properties with an increase in current density—an increase of 13.8% at 0.1mAcm−2 and 40.1% at 2.0mAcm−2—compared that observed for the undoped material. Thus, doped MnO2 exhibits promise as a cathode material for lithium primary batteries, and we determine that the electrochemical reaction process of Li+ insertion into the MnO2 matrix may be a mixed-controlled reaction. Based on an investigation of various depths of discharge, it is assumed that Sc2O3, TiO2 and V2O5-doped MnO2 have better structural stability because of the stronger Mn-O bond energy and smaller cell volume changes induced by doping. Moreover, a model has been proposed to describe the structural changes undergone by the test materials at different depths of discharge.